Amplifier applications requiring operation over a wide power range have typically utilized linear power amplifiers. Linear power amplifiers perform well at both low and high power levels. However, linear amplifiers are efficient only when their output voltage is either very low or near the power supply voltage. In an application such as a disc data storage device the power efficiency of a linear power amplifier can be as low as 35% or less.
A switching mode amplifier is more power efficient. Switching mode amplifiers saturate when they are turned on, providing high current at a voltage near the power supply voltage. When the switching amplifier is turned off, no current is conducted. Current is conducted only at a voltage near the power supply voltage and hence this method of amplification is typically very power efficient. In a switching mode amplifier, the amount of current conducted can be controlled by varying the duty cycle of the amplifier. This can be accomplished by various methods such as pulse width modulation. However, when the desired output voltage is small in comparison to the power supply voltage, the finite time required to switch the amplifier on and off becomes significant. In practice, this limits the dynamic range of switching amplifiers, making them impractical for applications requiring very low as well as high power levels.